Ice. Molecular model of ice, the solid form of water. Each water molecule is made up of one oxygen atom (red ball) bonded to two hydrogen atoms (white balls). The oxygen atoms have a slight negative charge, and the hydrogen atoms have small positive ones. The hydrogen atoms are attracted to oxygen atoms on neighbouring water molecules, forming weak bonds know as hydrogen bonds (light blue sticks). This leads to the rigid crystal structure of ice. The open structure of ice causes it to float as it is less dense than liquid water.